Epoxy resin mixtures for prepregs and composites based on phosphorus-modified epoxies, dicy and/or aminobenzoic compounds

ABSTRACT

Epoxy resin mixtures to produce prepregs and composites contain the following components: 
     a phosphorus-modified epoxy resin with an epoxy value of 0.02 to 1 mol/100 g, made up of structural units derived from 
     (a) polyepoxy compounds with at least two epoxy groups per molecule and 
     (b) phosphinic acid anhydrides, phosphonic acid anhydrides or phosphonic acid half-esters; 
     dicyandiamide and/or an aminobenzoic acid derivative as the hardener; 
     an amino hardening accelerator.

This application is a 371 of PCT/DE95/01136 Aug. 25, 1995.

BACKGROUND OF THE INVENTION

The invention concerns epoxy resin mixtures for producing prepregs andcomposites and also the prepregs and composites produced from theseepoxy resin mixtures.

Composites based on epoxy resins and organic or inorganic reinforcingmaterials have become extremely important in many areas of industry anddaily life. The reasons include first the relatively simple and reliableprocessing of epoxy resins and, second, the good level of mechanical andchemical properties of cured epoxy resin molded materials adapt them todifferent applications and to utilize the properties of all thematerials involved in the composite to advantage.

Epoxy resins are preferably processed to composites by way of theproduction of prepregs. For this purpose, organic or inorganicreinforcing materials or embedding components in the form of fibers,nonwovens and wovens or of flat shaped articles are impregnated with theresin. In most cases this is done with a solution of the resin in aneasy-to-evaporate or easy-to-volatilize solvent. The resulting prepregsmust not be tacky after this process, but they must not be fully curedeither, and instead the resin matrix should merely be in aprepolymerized state. Furthermore, the prepregs must have sufficientstability in storage. For example, at least three months' stability instorage is required for the production of circuit boards. In furtherprocessing to yield composites, the prepregs must also melt on atelevated temperatures and they must form a strong and durable bond underpressure with the reinforcing materials and embedding components as wellas the materials used for the composite, i.e., the cross-linked epoxyresin matrix must have a high interfacial adhesion with the reinforcingmaterials and embedding components as well as the materials to be bondedsuch as metals, ceramics, minerals and organic materials.

When cured, composites are generally required to have a high mechanicalstrength and thermal stability as well as a good chemical resistance andheat distortion and a high resistance to aging. For electronic andelectrotechnical applications, constantly high electric insulationproperties are also required, and there are various other additionalrequirements for special applications. For example, use as a circuitboard material requires a high dimensional stability over a widetemperature range, good adhesion to glass and copper, a high surfaceresistivity, a low dielectric loss factor, good machinability(punchability, drillability), low water absorption and a high corrosionresistance.

Flame resistance is a requirement that has become increasingly importantin recent times. In many areas, e.g., for construction materials foraircraft and automotive engineering and for vehicles in publictransportation, this requirement has top priority because of the risk tohumans and property. Flame resistance of circuit board materials isindispensable for electrotechnical and electronic applications inparticular because of the high value of the electronic componentsmounted on them.

Therefore, one of the strictest material tests, namely the V-0classification according to UL 94 V, must be passed to evaluateflammability. In this test, a test object is exposed to a defined flamepositioned vertically at its lower edge. The total burning time in tentests must not exceed 50 sec. This requirement is difficult to meet,especially when the material is thin, which is the case in electronics.Epoxy resin, which is used industrially throughout the world for FR4laminates, meets these requirements only because it contains approx. 30%to 40% ring-brominated aromatic epoxy components, based on the resin,i.e., approx. 17% to 21% bromine. Comparably high concentrations ofhalogen compounds are used for other applications, often combined withantimony trioxide as a synergist. The problem with these compounds isthat although they have excellent flame-retardant properties, they alsohave some highly objectionable properties. For example, antimonytrioxide is listed as a carcinogen, and not only does chemicaldecomposition of aromatic bromine compounds release free bromineradicals and hydrogen bromide, which are highly corrosive, but also whenhighly brominated aromatics in particular decompose in the presence ofoxygen, they form the highly toxic polybromine dibenzofurans andpolybromine dibenzodioxins. Disposing of brominated refuse and toxicwastes also poses considerable problems.

For these reasons, there has been no lack of attempts to replacebromine-containing fireproofing agents with less problematicalsubstances. For example, fillers with a extinguishing gas effect such asaluminum oxide hydrates (see "J. Fire and Flammability," vol. 3 (1972),pp. 51 ff.), basic aluminum carbonates (see "Plast. Engng." vol. 32(1976) pages 41 ff.) and magnesium hydroxides (European PatentApplication 243,201) as well as vitrifying fillers such as borates (see"Modern Plastics," vol. 47 (1970), no. 6, pages 140 ff.) and phosphates(U.S. Pat. No. 2,766,139 and U.S. Pat. No. 3,398,019) have beenproposed. However, all these fillers have the disadvantage that theyoften seriously impair the mechanical, chemical and electric propertiesof the composites. In addition, such fillers! require special processingtechniques which are usually more expensive because they have a tendencyto sediment and increase the viscosity of the resin system in which theyare used as fillers.

The flame-retardant effect of red phosphorus has already been described(British Patent 1,112,139), in some cases combined with extremely finelydivided silicon dioxide or aluminum oxide hydrate (U.S. Pat. No.3,373,135). This yields materials whose use for electronic andelectrotechnical purposes is limited because of the phosphoric acidformed in the presence of moisture and the resulting corrosion.Furthermore, organic phosphorus compounds such as phosphoric acidesters, phosphonic acid esters and phosphines have been proposed asflame-retardant additives (see: W. C. Kuryla and A. J. Papa "FlameRetardancy of Polymeric Materials," vol. 1, Marcel Dekker, Inc., NewYork, 1973, pages 24 to 38 and 52 to 61). However, this alternative hasnot been very promising, either, because these compounds are also knownfor their plasticizing properties and are used world-wide asplasticizers on a large scale (British Patent 10,794).

To achieve a flame resistance that complies with UL 94 V-0, it is knownfrom German Patent Application 3,836,409 that prepregs can be producedby impregnating certain reinforcing materials or flat shaped articlesusing a suspension of halogen-free fire-proofing agents containingnitrogen and phosphorus in a solution of aromatic, heterocyclic and/orcycloaliphatic epoxy resins (in ring-halogenated form or anon-ring-halogenated form with a low halogen content) and aromaticpolyamines and/or aliphatic amides as the hardener. The fireproofingagents here are halogen-free melamine resins or organic phosphoric acidesters, specifically melamine cyanurates, melamine phosphates, triphenylphosphate and diphenyl cresyl phosphate as well as mixtures thereof.However, this is not a very promising solution because these fillersalways increase water absorption and therefore the products cannot passspecific tests for circuit boards.

Organic phosphorus compounds that can be anchored in the epoxy resinnetwork such as phosphorus compounds containing epoxy groups can also beused to make epoxy resins flame retardant. For example, European Patent384,940 discloses epoxy resin mixtures containing commercially availableepoxy resin, the aromatic polyamine1,3,5-tris(3-amino-4-alkylphenyl)-2,4,6-trioxohexahydrotriazine and anepoxy group-containing phosphorus compound based on glycidyl phosphate,glycidyl phosphonate or glycidyl phosphinate. Flame-retardant laminatesor composites that can be classified according to UL 94 V-0 --without ahalogen additive--and have a glass transition temperature of >200° C.can be produced with such epoxy resin mixtures. In addition, these epoxyresin mixtures can be processed by methods comparable to those used withthe epoxy resins currently in use.

Circuit boards form the basis for manufacturing electronic assemblies.They are used to connect a wide variety of electronic andmicroelectronic components to form electronic circuits. The componentsare mounted on the circuit board by gluing or soldering using complex,highly automated assembly processes. There is also a trend towardincreasingly economic manufacturing methods in assembly of printedcircuit boards.

Therefore, IR reflow soldering is being used increasingly in SMDtechnology and will largely replace other soldering techniques in thefuture. In this process, the entire circuit board is heated by IRirradiation to temperatures >260° C. within a few seconds. Waterabsorbed in the circuit board is then vaporized all at once. Onlylaminates with very good interlaminar adhesion will withstand IRsoldering processes without being destroyed by delamination. To reducethis risk, expensive conditioning processes have been proposed (see"Galvanotechnik" vol. 84 (1993) pages 3865-3870).

In this regard, mainly the so-called multilayer circuit boards (ML),which constitute a majority of the circuit boards produced today, arecritical. Such circuit boards include several structured conductorplanes which are spaced and insulated with respect to each other byepoxy resin composites. The trend in multilayer circuit board technologyis toward larger and larger numbers of structured conductor planes. Thusmultilayer circuit boards with more than 20 structured conductor planesare manufactured at the present. Since an excessive overall thickness ofthese circuit boards must be avoided for technical reasons, the distancebetween the structured conductor planes has become smaller and smallerand thus the interlaminar adhesion and the copper adhesion in multilayercircuit board laminates has also become more problematical. In IRsoldering, especially high demands are also made on this type of circuitboards with regard to solder bath resistance.

As stated above, it is already known from European Patent 384,940 thatlaminates with the required high flame resistance can be producedwithout halogen by phosphorus modification of impregnating resins. Inmanufacturing experiments, however, it has been found that there is arisk of delamination in IR soldering with phosphorus-modified laminates.Therefore, there is an urgent need for electrolaminates where therequired flame resistance is achieved without the use of halogens, e.g.,by incorporating phosphorus into the resin matrix, but where thelaminates are suitable for IR soldering, which has been introduced intoSMD technology. Electro laminates with an extremely high solder bathresistance are needed for this purpose.

In circuit board technology, mainly the high-pressure cooker test (HPCT)and the determination of the solder bath resistance are used to test thesuitability of laminates for a high thermal stressing. In HPCT alaminate sample (5×5 cm) from which copper has been removed is stressedfor two hours at 120° C. under a steam pressure of approx. 1.4 bar andthen stored floating in a solder bath at 260° C., and the time untildelamination is measured. Good quality laminates do not show anydelamination for up to >20 sec under these conditions. The solder bathresistance is determined on 2×10 cm laminate specimens which areimmersed in a solder bath at 288° C. and the time until delamination ismeasured.

Adequate stability of the base materials in storage is another importantrequirement for industrial use. This is true in particular for prepregsfor manufacturing multilayer circuit boards. Special copper-laminatedinner layers are pressed with prepregs and copper foils. A preciselyadjusted reactivity and optimum flow properties are prerequisites in thecompression molding process to produce multilayer circuit boards withoptimum interlaminar adhesion and thus a solder bath resistance towithstand IR soldering processes without risk of destruction due todelamination. These processing properties are achieved in thesemifinished products. To assure that the processing properties arestill met in the manufacture of multilayer circuit boards, a storagestability of >3 months is required of the prepregs. The reactivity mustnot change more than 10% within this period of time. So far it has beendifficult to meet this requirement with halogen-free flame-retardantcircuit board base materials. Thus, the storage stability of prepregscan be impaired by measures for incorporating organic phosphoruscomponents and for improving interlaminar adhesion and solder bathresistance.

SUMMARY OF THE INVENTION

The object of this invention is to provide technically simple and thusinexpensively accessible epoxy resin mixtures that can be processed bymethods comparable to those used with the epoxy resins in industrial useand--thanks to the required stability in storage--are suitable forproducing prepregs and laminates for the multilayer technology thatyield flame-retardant molded materials (i.e., classifiable according toUL 94 V specifications) without halogen additives while at the same timehaving such a great solder bath resistance that IR soldering processesare possible without delamination.

DETAILED DESCRIPTION OF THE INVENTION

This is achieved according to this invention by the fact that the epoxyresin mixtures contain the following components:

a phosphorus-modified epoxy resin with an epoxy value of 0.02 to 1mol/100 g, made up of structural units derived from:

(A) polyepoxy compounds with at least two epoxy groups per molecule and

(B) phosphinic acid anhydrides, phosphonic acid anhydrides or phosphonicacid half-esters;

dicyandiamide and/or an aromatic amine of the following structure as ahardener: ##STR1## where X denotes a hydrogen atom and Y is an alkylgroup with 1 to 3 C atoms, and m and n each denote an integer from 0 to4 with the provision that m+n=4,

R is an OH group or an NR¹ R² group, where the R¹ group and the R2 groupindependently of each other denote a hydrogen atom, an alkyl group with1 to 3 C atoms or an aralkyl group, or one of the R¹ and R² groups hasthis meaning and the other denotes an NR³ R⁴ group, R³ and R⁴ =H or analkyl with 1 to 3 C atoms, or R1 and R² together with the nitrogen forma heterocyclic group;

an amino hardening accelerator.

The phosphorus-modified epoxy resins contained in the epoxy resinmixtures according to the invention are produced by reactingconventional commercial polyepoxy resins (polyglycidyl resins) with thefollowing phosphorus compounds:

phosphinic acid anhydrides: anhydrides of phosphinic acids with alkyl,alkenyl, cycloalkyl, aryl or aralkyl groups; examples include dimethylphosphinic acid anhydride; methylethyl phosphinic acid anhydride,diethyl phosphinic acid anhydride, dipropyl phosphinic acid anhydride,ethylphenyl phosphinic acid anhydride and diphenyl phosphinic acidanhydride;

bisphosphinic acid anhydrides: anhydrides of bisphosphinic acids, inparticular alkanebisphosphinic acids with 1 to 10 carbons in the alkanegroup;

examples include methane-1,1-bismethyl-phosphinic acid anhydride,ethane-1,2-bismethyl-phosphinic acid anhydride,ethane-1,2-bisphenyl-phosphinic acid anhydride andbutane-1,4-bismethyl-phosphinic acid anhydride;

phosphonic acid anhydrides: anhydrides of phosphonic acids with alkyl,alkenyl, cycloalkyl, aryl or aralkyl groups;

examples include methanephosphonic acid anhydride, ethanephosphonic acidanhydride, propanephosphonic acid anhydride, hexanephosphonic acidanhydride and benzenephosphonic acid anhydride;

phosphonic acid half-esters: preferably, half-esters, i.e. monoesters ofphosphonic acids with alkyl groups (preferably with 1 to 6 C atoms) orwith aryl groups (in particular benzenephosphonic acid) with aliphaticalcohols, in particular low-boiling aliphatic alcohols, such as methanoland ethanol are used;

examples include methanephosphonic acid monomethyl ester,propanephosphonic acid monoethyl ester and benzenephosphonic acidmonomethyl ester.

Phosphonic acid half-esters can be synthesized by partial hydrolysis ofthe corresponding phosphonic acid diesters, in particular by means ofsodium hydroxide solution, or by partial esterification of the freephosphonic acids with the corresponding alcohol.

Synthesis of phosphorus-modified epoxy resins of this type is alsodescribed in German Patent Applications Nos. 4,308,184 and 4,308,185.

In general, both aliphatic and aromatic glycidyl compounds as well asthe mixtures thereof can be used to produce phosphorus-modified epoxyresins. Preferred are bisphenol A diglycidyl ether, bisphenol Fdiglycidyl ether and polyglycidyl ethers of phenol-formaldehyde andcresol-formaldehyde novolaks, diglycidyl esters of phthalic acid,isophthalic acid, terephthalic acid and tetrahydrophthalic acid as wellas mixtures of these epoxy resins. Other polyepoxides that can be usedare described in the "Handbook of Epoxy Resins" by Henry Lee and KrisNeville, McGraw-Hill Book Company, 1967, and in the monograph "EpoxyResins" by Henry Lee, American Chemical Society, 1970.

Of the range of possible phosphorus-modified epoxy resins, those thathave proven especially favorable for the production of electrolaminatesthat are stable in a solder bath include phosphonic acid-modified epoxyresins such as methyl, ethyl and propyl phosphonic acid-modified epoxyresins, in particular with a phosphorus content between 2 and 5 wt %. Inaddition, phosphorus-modified epoxy resins with an average of at leastone epoxy functionality, in particular those with an average of at leasttwo epoxy functionalities are advantageous. Such phosphorus-modifiedepoxy resins can be produced by reacting epoxy novolak resins with afunctionality of approx. 3 to 4 with phosphonic acid anhydrides. Thephosphorus-modified epoxy resins contain 0.5 to 13 wt % phosphorus,preferably 1 to 8 wt %. The total phosphorus content of the epoxy resinmixtures, i.e., the impregnation resin mixtures, is 0.5 to 5 wt %,preferably 1 to 4 wt %.

The epoxy resin mixtures according to this invention preferably alsocontain a phosphorus-free epoxy resin or a glycidyl group-free compoundwith phenolic OH groups. The phosphorus-free epoxy resin is obtained byreacting bisphenol A diglycidyl ether with a substoichiometric quantityof bisphenol A. The glycidyl group-free compound is bisphenol A,bisphenol F or a high-molecular phenoxy resin synthesized bycondensation of bisphenol A or bisphenol F with epichlorohydrin.

Adding the phosphorus-free epoxy resin serves to achieve certainproperties in the laminates produced from the epoxy resin mixtures. Theproduction and structure of such solid resins are described in H. Batzer"Polymer Materials," vol. III(Technology 2), Georg Thieme Verlag,Stuttgart 1984, pages 178 ff. These are high-molecular, chain-lengthenedbisphenol A diglycidyl ethers with an epoxy value of 0.22 to 0.29equivalents per 100 g. Phosphorus-free epoxy resins with an epoxy valueof 0.22 to 0.25 equivalents per 100 g are preferably used in the epoxyresin mixtures according to this invention. The viscosity of theseresins, measured at 120° C., is between 300 and 900 mPa·s. The totalphosphorus-free epoxy resin content of the epoxy resin mixture isbetween 0 and 30 wt %, preferably between 0 and 10 wt %. Thephosphorus-free epoxy resin component may be added only in an amountsuch that the total phosphorus content of the mixture is stillsufficient to meet the flame resistance requirement according to the UL94 V. Therefore, more phosphorus-free epoxy resin can be added in thepresence of phosphorus-modified epoxy resins having a high phosphoruscontent than in the case of epoxy resins with a low phosphorus content.

The glycidyl group-free compound with phenolic OH groups is also addedto achieve certain properties. Bisphenol A and bisphenol F as well asphenoxy resins are used for this purpose. These are linear condensationproducts of bisphenol A or bisphenol F and epichlorohydrin in the formof high-molecular compounds with a molecular weight of up to 30,000. Theterminal phenolic OH function content is very low at <<1%. Synthesis andproperties of such phenoxy resins are known (see "Encyclopedia ofPolymer Science and Engineering" (second edition), vol. 6, pages 331 and332, John Wiley & Sons, Inc. 1986). The compound with phenolic OH groupsis added to the epoxy resin mixtures according to this invention inamounts of 0 to 20 wt %, preferably 0 to 10 wt %. Here again, it shouldbe recalled that the glycidyl group-free phenolic component may be addedonly up to an amount at which the flame resistance requirement accordingto the UL 94 V specification is met.

The hardener used in the epoxy resin mixtures according to thisinvention is dicyandiamide and/or a second hardener component based onaminobenzoic acid. Examples of this hardener component include2-aminobenzoic acid, 4-aminobenzoic acid, 4-amino-2-methylbenzoic acid,4-aminobenzoic acid amide, 4-aminobenzoic acid dimethyl amide and4-aminobenzoic acid hydrazide, where 4-aminobenzoic acid is preferred.Both dicyandiamide and the second hardener component may be used alone,but it is also advantageous to use hardener mixtures, where mixtures ofdicyanodiamide and 4-aminobenzoic acid are preferred, especially in aweight ratio of 3.5:1 to 2:1. If prepregs and laminates are producedfrom epoxy resin mixtures according to this invention containing such ahardener mixture, they surprisingly yield an optimum combination of theproperties that are important industrially for prepregs, such as solderbath resistance and storage stability.

The hardener is used in a concentration such that the equivalent ratiobetween the epoxy function and the active hydrogen function (NH or COOHfunction) in the epoxy resin mixtures according to this invention is1:0.4 to 1:1.1, preferably 1:0.5 to 1:0.8. It should be pointed out thatwhen a phosphorus-free phenolic component is added, the concentration ofepoxy groups is reduced according to the phenolic OH group content. Ingeneral, the hardener content of the resin mixture is 0.5 to 35 wt %,preferably 2 to 12 wt %.

Japanese Patent Application 58-142913 discloses resin compositionscontaining polymaleimides, aminobenzoic acid amides and epoxy resins.These compositions are suitable for producing glass laminates, butwithout halogen these laminates do not have a flame resistance thatwould comply with UL 94 V.

The tertiary amines and imidazoles conventionally used to cure epoxyresins are used as the amino hardening accelerators. Suitable aminesinclude, for example, tetramethylethylenediamine, dimethyloctylamine,dimethylaminoethanol, dimethylbenzylamine,2,4,6-tris(dimethylaminomethyl)phenol, N,N'-tetramethyl-diaminodiphenylmethane, N, N'-dimethylpiperazine, N-methyl -morpholine,N-methylpiperidine, N-ethylpyrrolidine, 1,4-diazabicyclo 2.2.2!octaneand quinolines. Suitable imidazoles include, for example,1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole,1,2,4,5-tetramethylimidazole, 2-ethyl -4-methylimidazole,1-cyanoethyl-2-phenylimidazole and1-(4,6-diamino-s-triazinyl-2-ethyl)-2-phenylimidazole. The acceleratoris used in a concentration of 0.01 to 2 wt %, preferably 0.05 to 1 wt %,each based on the epoxy resin mixture.

To prepare the prepreg, the various components, either separately ortogether, are dissolved in inexpensive solvents such as acetone, methylethyl ketone, ethyl acetate, methoxyethanol, dimethylformamide andtoluene or in mixtures of such solvents, optionally combined to onesolution. The solution is then processed on conventional impregnationfacilities, i.e., for impregnating fibers of organic or inorganicmaterials such as glass, metal, minerals, carbon, aramide, polyphenylenesulfide and cellulose as well as the woven or nonwoven fabrics producedfrom them or for coating flat shaped articles such as films of metals orplastics. The impregnation solutions may optionally also containadditional halogen-free additives to improve the flame resistance, someof which may be homogeneously dissolved or dispersed. Such additives mayinclude, for example, melamine cyanurates, melamine phosphates,pulverized polyether imide, polyether sulfone and polyimide.

Mainly glass fiber fabric is used to produce prepregs for circuit boardtechnology. In particular, types of glass fiber fabric with a surfacedensity of 25 to 200 g/m² are used for multilayer circuit boards.Prepregs with low surface densities can also be produced to conform torequirements with impregnation solutions of the type described above.The impregnated or coated reinforcing materials and embedding componentsare dried at an elevated temperature at which the solvent is removedwhile at the same time the impregnation resin undergoesprepolymerization. On the whole this yields an extraordinarily favorableratio of cost to achievable properties.

The resulting coatings and prepregs are not tacky and they are stable instorage for three months or more at room temperature, i.e., they have anadequate stability in storage.

They can be processed by compression molding at temperatures up to 220°C. to yield composites that are characterized by high glass transitiontemperatures of up to 170° C. and by an inherent flame resistance. Forexample, if glass fiber fabric with a percentage by mass content of 60%through 62%, based on the laminate, is used as the embedding material,it will pass the UL 94 V burning test with a safe V-0 classificationwithout the addition of halogen compounds or other flame-retardantadditives--even if the test object has a wall thickness of 1.6 mm oreven 0.8 mm. It has proven to be especially advantageous that nocorrosive or especially toxic cleavage products are formed and much lesssmoke is generated in comparison with other polymer materials, inparticular bromine-containing epoxy resin molded compounds.

The laminates produced from the epoxy resin mixtures according to thisinvention, in particular when a hardener mixture is used, arecharacterized by a combination of good properties attractive forindustrial use, such as the adhesive strength to copper, interlaminaradhesion, solder bath resistance and stability in storage.

This invention will now be illustrated in greater detail on the basis ofpractical embodiments (all parts are parts by weight).

EXAMPLE 1 Production of prepregs

A solution of A parts dicyandiamide (DCD) in H parts dimethylformamide(DMF) is mixed with a solution of C parts of a phosphorus-modified epoxyresin (P/EP resin) in the form of a reaction product (epoxy value 0.32mol/100 g; phosphorus content 3.8%) of an epoxidized novolak (epoxyvalue 0.56 mol/100 g; average functionality 3.6) and propanephosphonicacid anhydride in G parts methyl ethyl ketone (MEK) and I parts ethylacetate (EA). Then D parts 2-methylimidazole (MeIm) are added to theresin solution. Glass fiber fabrics (fabric type 7628, surface density197 g/m²) are impregnated continuously with the resulting impregnationresin solution on a laboratory impregnation installation and then driedin a vertical dryer at temperatures of 50° C. to 1600° C. Prepregsproduced in this way are tack-free. Table 1 shows the composition of theimpregnation resin solution and the properties of the prepregs.

EXAMPLES 2 THROUGH 5 Production of prepregs

The procedure described in Example 1 is followed, but the impregnationresin solutions are also mixed with B parts 4-aminobenzoic acid (ABA)and E parts of an epoxy resin (EP resin) dissolved in J partsdimethylformamide (DMF). The epoxy resin (epoxy value 0.25 mol/100 g;viscosity at 120° C. 380 mPa·s) is produced by reacting bisphenol Adiglycidyl ether with a substoichiometric quantity of bisphenol A. Table1 shows the composition of the impregnation resin solutions and theproperties of the prepregs.

EXAMPLE 6 Production of prepregs

The procedure described in Example 1 is followed, but the impregnationresin solution is also mixed with B parts 4-aminobenzoic acid (ABA) andF parts of a phenoxy resin (phen resin) dissolved in J partsdimethylformamide (DMF). The phenoxy resin (molecular weight 25,000 to30,000; hydroxyl value 6%) is a glycidyl group-free linear condensate ofbisphenol A and epichlorohydrin. Table 1 shows the composition of theimpregnation resin solution and the properties of the prepregs.

                  TABLE 1                                                         ______________________________________                                        Composition of the impregnation resin                                         solutions and properties of the prepregs                                      Example                                                                       no.      1      2      3     4    5    6     7                                ______________________________________                                        Components                                                                    (parts)                                                                       A (DCD)  4.9    3.5    3.0   3.0  2.5  3.0   --                               B (ABA)  --     1.0    1.5   2.0  3.0  1.5   12                               C (P/EP  95     85     86    85   84   86    88                               resin)                                                                        D (MeIm) 0.1    0.1    0.1   0.1  0.1  0.1   --                               E (EP    --     10     10    10   10   --    --                               resin)                                                                        F (phen  --     --     --    --   --   10    --                               resin)                                                                        G (MEK)  66     70     70    70   70   50    66                               H (DMF)  29     6      6     6    6    6     30                               I (EA)   5      4      4     4    4    4     4                                J (DMF)  --     20     20    20   20   40    --                               Measured                                                                      values:                                                                       Residual 0.2    0.2    0.2   0.2  0.2  0.2   0.2                              solvent                                                                       content                                                                       (%)                                                                           Residual 90     93     90    75   30   60    gelled                           gel                                                                           time after                                                                    3 months                                                                      (in % of                                                                      starting                                                                      value)                                                                        ______________________________________                                    

The residual gel time is determined by applying glass fiber-freeimpregnation resin (0.2 to 0.3 g) mechanically separated from theprepregs to a hot plate preheated to 170° C. After approx. 30 sec, thefused resin specimen is stirred uniformly with a glass or wooden rod.The change in viscosity is observed by pulling approximately 50 mm longfilaments out of the melt. Gelation has occurred if no filaments can bepulled any longer. The gel time is the period of time (in seconds)determined with a stop watch from applying the resin to the hot plateuntil the premature breaking of the filaments.

EXAMPLE 7 Comparative experiment

The procedure in Example 1 is followed, but the impregnation resinsolution is mixed with B parts 4-aminobenzoic acid (ABA) dissolved in Hparts dimethylformamide (DMF)--instead of A parts dicyandiamide (DCD).In addition, no hardening accelerator (D) is added. Table 1 shows thecomposition of the impregnation resin solution and the properties of theprepregs.

EXAMPLE 8 THROUGH 14 Producing and testing laminates

Eight of each prepreg produced according to Examples 1 through 7 (glassfiber fabric type 7628, surface density 197 g/m²), laminated on bothsides with a 35 μm copper foil, are pressed by compression molding in apress at 175° C. and 20 bar. The 1.5 to 1.6 mm thick laminates areremoved from the press after 40 minutes and then after-baked for 2 hoursat 175° C. The glass transition temperature T_(G) is determined on theresulting test objects by dynamic mechanical analysis (DMTA), inaddition to determining the flammability according to UL 94 V, theadhesion of the copper foil, the Measling test, the high-pressure cookertest and the solder bath resistance. Table 2 shows the values thusobtained.

                  TABLE 2                                                         ______________________________________                                        Properties of the laminates                                                   Example no. 8      9      10   11   12   13   14                              ______________________________________                                        Prepregs acc.                                                                             1      2      3    4    5    6    7                               to example No.                                                                Measured values                                                               T.sub.G (°C.)                                                                      170    168    161  156  160  155  160                             Average     2.7    4.7    4.9  4.7  4.8  4.4  3.9                             burning time acc.                                                             to UL 94 V (sec)                                                              Classification                                                                            V-0    V-0    V-0  V-0  V-0  V-0  V-0                             Adhesion of the                                                                           48     52     53   49   49   51   47                              of the copper foil                                                            at room temp. (N/mm)                                                          Measling test                                                                             +      +      +    +    +    +    +                               (LT26)                                                                        High-pressure                                                                             12     18     >20  >20  >20  >20  >20                             cooker test (sec)                                                             Solder bath 50     115    115  125  144  95   >600                            resistance at 288° C.                                                  (sec)                                                                         ______________________________________                                    

The tests performed on the laminates were carried out as follows:

Adhesion of the copper lamination

A 25 mm-wide and 100 mm-long strip of the copper foil is separated fromthe glass-reinforced laminate for a length of 20 mm and pulled awayvertically at a pull-away speed of 50 mm/min using a suitable device.The force F (N) required to accomplish this is measured.

Measling test

The test is performed on test objects without copper lamination (size:20 mm×100 mm). The test objects are immersed for 3 minutes in a 65° C.LT26 solution (composition: 850 ml deionized water, 50 ml HCl,analytical purity, 100 g SnCl₂ ·2H₂ O, 50 g thiourea), rinsed withrunning water and then placed in boiling water for 20 minutes. Afterdrying in air (2 to 3 minutes), the sample is immersed in a solder bathat 260° C. for 10 seconds. The laminate must not delaminate in thistest.

High-pressure cooker test

Two test objects measuring 50 mm ×50 mm are stored in a steam atmosphereat a temperature of 120°-125° C. in a high-pressure autoclave for twohours. Then within 2 minutes, the dried samples are placed in a solderbath at 260° C. for 20 seconds. The test objects must not delaminate.

Solder bath resistance

This test is performed according to DIN IEC 259 using a solder bathaccording to section 3.7.2.3, using test objects measuring 25 mm ×100 mmthat are immersed in a solder bath at a temperature of 288° C., and thetime until delamination occurs or bubbles develop is measured.

What is claimed is:
 1. An epoxy resin mixture for producing prepregs andcomposites, comprising:a phosphorus-modified epoxy resin with an epoxyvalue of 0.02 to 1 mol/100 g, which is a reaction product of(a)polyepoxy compounds with at least two epoxy groups per molecule, and (b)phosphinic acid anhydrides, phosphonic acid anhydrides or phosphonicacid half-esters; dicyandiamide and/or an aromatic amine of thefollowing structure as a hardener: ##STR2## where X is a hydrogen atomand Y is an alkyl group with 1 to 3 C atoms, and m and n denote aninteger from 0 to 4 where m+n=4,R is an OH or NR¹ R² group, where the R¹and R² groups, independently of each other, denote a hydrogen atom, analkyl group with 1 to 3 C atoms or an aralkyl group or one of the R¹ andR² groups has this meaning and the other group is an NR³ R⁴ group, whereR³ and R⁴ =H or an alkyl group with 1 to 3 C atoms, or R¹ and R²together with the nitrogen may form a heterocyclic group; and an aminohardening catalyst.
 2. Epoxy resin mixture according to claim 1, whichcontains a phosphorus-free epoxy resin prepared by reacting bisphenol Adiglycidyl ether with a substoichiometric quantity of bisphenol A, or aglycidyl group-free compound with phenolic OH groups selected from thegroup consisting of bisphenol A, bisphenol F and a phenoxy resinobtained by condensation of bisphenol A or bisphenol F withepichlorohydrin.
 3. Epoxy resin mixture according to claim 2, whereinthe phosphorus-free epoxy resin content in the resin mixture is up to 30wt %.
 4. Epoxy resin mixture according to claim 3, wherein thephosphorus-free epoxy resin content in the resin mixture is up to 10 wt%.
 5. Epoxy resin mixture according to claim 2, wherein the amount ofthe glycidyl group-free compound in the resin mixture is up to 20 wt %.6. Epoxy resin mixture according to claim 5, wherein the amount of theglycidyl group-free compound in the resin mixture is up to 10 wt %. 7.Epoxy resin mixture according to claim 1, wherein the phosphorus contentis 0.5 to 5 wt %, based on the resin mixture.
 8. Epoxy resin mixtureaccording to claim 7 wherein the phosphorus content is 1 to 4 wt %,based on the resin mixture.
 9. Epoxy resin mixture according to claim 1,wherein the equivalent ratio between epoxy functions and NH functions is1:0.4 to 1:1.1.
 10. Epoxy resin mixture according to claim 9 wherein theequivalent ratio between epoxy functions and NH functions is 1:0.5 to1:0.8.
 11. Epoxy resin mixture according to claim 1, wherein thehardener content of the resin mixture is 0.5 to 35 wt %.
 12. Epoxy resinmixture according to claim 11, wherein the hardener content of the resinmixture is 2 to 12 wt %.
 13. Epoxy resin mixture according to claim 1,wherein the hardener is 2-aminobenzoic acid, 4-aminobenzoic acid,4-amino-2-methylbenzoic acid, 4-aminobenzoic acid amide, 4-aminobenzoicacid dimethylamide or 4-aminobenzoic acid hydrazide.
 14. A prepreg basedon organic or inorganic reinforcing materials in the form of fibers,wovens or nonwovens or flat shaped articles, produced from the epoxyresin mixture according to claim
 1. 15. A composite based on organic orinorganic reinforcing materials in the form of fibers, wovens ornonwovens or flat shaped articles, produced from the epoxy resin mixtureaccording to claim
 1. 16. A circuit board made of prepregs, producedfrom glass fiber fabrics and the epoxy resin mixture according toclaim
 1. 17. Epoxy resin mixture according to claim 1, wherein thehardener is a mixture of dicyandiamide and 4-aminobenzoic acid.